Resistance and modulus reinforcing materials

ABSTRACT

This invention relates to new composite materials having, along a director plane, noteworthy mechanical properties, wherein they comprise a resistant material, in flat form disposed parallel to the director plane and flakes or bands or substantially flat form, constituted of or comprising a material with high modulus, said flakes or bands also being disposed parallel to the director plane.

The present invention relates to new composite materials having, along adirector plane, a high breaking strength and a high modulus.

It is known to produce composite materials having high specificproperties along a preferred direction by incorporating fibers having ahigh modulus of elasticity in a simple or composite matrix that may havea high tensile strength.

The invention relates to new composite materials having, along adirector plane, particularly high mechanical properties, wherein saidmaterials comprise a resistant material, in sheets, disposed parallel tothe director plane and substantially flat flakes or bands made of amaterial with a high modulus, said flakes or bands also being disposedparallel to the director plane.

The materials according to the invention may also comprise at least onematerial forming a matrix capable of ensuring a good cohesion betweenthe resistant materials with high modulus.

As resistant material, in substantially flat sheets, use is preferablymade of sheets of steel, titanium or alloys based on nickel, whosethickness may vary from 1μ to about 1 mm. The sheets of steel,preferably steel of the maraging type, may, in the composite material,be in the form of continuous sheets or in the form of discontinuousplates of relatively reduced dimensions. The essential point is thatthey are disposed parallel to the selected director plane. These steelor titanium sheets may possibly be coated superficially, before beingused in the complex materials according to the invention, with amaterial capable of acting as matrix, such as for example a resin, analloy or a light metal of the aluminium or magnesium type.

The modulus reinforcing material may be constituted of:

A. Flakes of elements such as boron, silicon carbide, titanium diboride,aluminium or magnesium diboride.

These flakes may be used in the crude state, in which case they aredistributed as uniformly as possible on a metal or plastic sheetconstituting the matrix or directly on the resistance reinforcingmaterial.

B. Continuous or non-continuous bands coated on one side or on bothsides with a film of thickness between 1 and 500μ of light elements witha very high modulus such as silicon carbide, boron, boron carbide,titanium diboride, etc. generally of compounds of light elements. It isknown to prepare such coated bands. In fact, for the silicon carbide orboron coating, the technique of deposit in vapour phase may be used forexample, the band then being constituted in general by a refractorymetal such as tungsten, tantalum, molybdenum . . . of small thickness(thickness smaller than 50μ). This band is heated in a reactor in thepresence of adequate gases. Techniques of evaporation in vacuo may alsobe used. The element to be evaporated, such as boron or boron carbide,is contained in a crucible and taken to very high temperature. Duringevaporation, it is deposited on a continuous or non-continuous ribbon ofthe matrix material or directly on the resistance reinforcing material.

The composite material is then constituted by the superposition ofresistance reinforcing materials and of modulus reinforcing product.These two elements may or may not be separated by a third matrixmaterial whose aim, in certain applications, is to limit the fragilityand to ensure the cohesion of the whole. This matrix may be constitutedby a resin or a metal or alloy such as magnesium, aluminium, andgenerally all materials of low density.

The superposition of these different types of materials may be regular,the resistance reinforcing materials alternating with the modulusreinforcing products, separated or not by a matrix material. Theregularity of this alternance is not absolutely necessary and, forconsiderations of specific volumetric fractions of each of the uses, aplurality of layers of modulus reinforcing material may be superposedwithout separation. The invention relates to all the possible modes ofsuperposing the three elements: resistance reinforcing elements, modulusreinforcing elements and matrix.

Of course, the resistant materials and the materials with high modulusused according to the invention, although they generally have a flatstructure, may be in the physical form which gives them improvedproperties, such as for example in the corrugated form.

However, it has appeared that, according to the invention, a certainnumber of composite materials had especially advantageous properties.Such materials are characterised on the one hand by the choice of thebasic elements which compose them and on the other hand by theconditions under which they are prepared, which conditions permit thedevelopment of beneficial interactions between a certain number ofconstituents of said materials.

These noteworthy composite materials are:

1. The composite materials in which the matrix is constituted bytitanium and the reinforcing elements by flakes or bands whose surfaceis made of silicon carbide; in the case of the reinforcing materialbeing constituted of bands with silicon carbide surface, said bands areformed by depositing silicon carbide on a molybdenum or preferablytitanium core, said deposit being effected by high temperature reactionof a gaseous mixture comprising a silane, a saturated hydrocarbon andhydrogen.

2. The composite materials in which the matrix is made of aluminium andthe reinforcing elements are flakes or bands whose surface is boron ormade of boron-rich compounds.

In these two types of composite materials according to the invention, itseems in fact that by using particular conditions of preparation, abeneficial interaction is effected between the matrix and the materialforming the surface of the reinforcing element. These conditions ofpreparation must therefore aim at producing such interactions.

Where the matrix is made of titanium and the surface of the reinforcingmaterial is made of silicon carbide, the various materials that aresuitably disposed (flat orientation according to the invention) will bepressed at a temperature of about 900° C. under a pressure of about 4kg./mm.² for a sufficient duration for the interaction between thetitanium and silicon carbide (with formation of various materials suchas titanium carbide and titanium silicide) to develop.

The present means for investigation only enable such an interaction tobe detected with certitude, in this particular case, when the process ofinteraction has a thickness of at least 1μ. It is known that a processof interaction of the same type is also developed when the reinforcementof a titanium matrix is effected with the aid of fibres whose surface ismade of silicon carbide. However, there is a basic difference betweenthe reinforcement of titanium by fibres with silicon carbide surface andby flakes or bands with silicon carbide surface. In fact, it has beendemonstrated that by using the reinforcement by fibres, the interactionbetween the titanium and the silicon carbide was prejudicial for thefinal material as soon as such an interaction was detectable, i.e. assoon as its thickness was equal to 1μ. In the case of a reinforcement byflakes or bands with silicon carbide surface, such an interaction, evenof thickness at least equal to 1μ, i.e. detectable, is beneficial.

Where the matrix is made of aluminium and the surface of the reinforcingmaterial is made of boron or boron-rich compounds, the two materialswill be pressed under a pressure of about 3 kg./mm.² and at atemperature of 580° C. ± 10° C. for a duration of the order of 1 hour to11/2 hours, so that a layer of aluminium diboride (AlB₂) is producedwhich must be of the order of a few fractions of microns.

The following non-limiting examples illustrate the invention; in theseexamples, the following properties have been given for the compositematerial obtained; the density (d), tensile strength (R) and the modulusof elasticity (E), these latter two properties being measured in adirection parallel to the director plane.

EXAMPLE 1

Composite materials are produced which are constituted of a resistancereinforcing element made of maraging steel, a modulus reinforcingelement obtained by flakes of aluminium diboride deposited on a sheet ofresin and a matrix made of aluminium. For the same volumic fractions aspreviously,

    d=4.2

    R=130 kg./mm..sup.2

    E=22,000 kg./mm..sup.2

EXAMPLE 2

Composite materials are produced which are constituted of a resistancereinforcing element made of eutectoid steel with 0.8% carbon, a modulusreinforcing element made of silicon carbide deposited on a tungstenribbon, a magnesium matrix. For the same volumic fractions aspreviously,

    d=4.6

    R=140 kg./mm..sup.2

    E=26,000 kg./mm..sup.2

EXAMPLE 3

Composite materials are produced which are constituted by an aluminiummatrix and reinforcing elements which are flakes of aluminium diborideby coating said flakes, suitably placed between flat aluminium sheets,by means of aluminium. This coating, without apparent chemical reactionon the interface of the materials, is obtained by pressing saidmaterials at a temperature of the order of 630° C.

EXAMPLE 4

A composite material is produced which is constituted by a titaniummatrix and a reinforcing element constituted by a band obtained bydepositing silicon carbide on titanium. These two constituents aresuitably disposed and subjected to a pressure of 4 kg./mm.², at atemperature of about 900° C. for a prolonged duration.

The materials obtained have respectively:

for a V_(f) =50% a modulus (E) of 25,000 kg./mm.² and a density of 3.6;

for a V_(f) =80% a modulus of 34,000 kg./mm.² and a density of 3.3,V_(f) being the volumic fraction (the percentage in volume) of thereinforcing element (possible substrate included in the complex materialin question.

EXAMPLE 5

A composite material is produced which is constituted by an aluminiummatrix and a reinforcing element constituted by boron flakes. Afterbeing placed in position, the whole is heated under a pressure of 3kg./mm.² to a temperature of 590° C. for 11/2 hours. A material has beenobtained having noteworthy properties in which an intermediate material(AlB₂) appears, coming from the interaction between the aluminium andboron.

Of course, the composite materials such as described in Examples 3 and 5will also have to comprise a resistance reinforcing material as definedhereinabove, as the aluminium has a mechanical resistance which isgenerally considered to be low.

What is claimed is:
 1. A composite material having improved mechanical properties comprising, a resistant material, a reinforcing material with high modulus and a matrix material, said resistant material is flat, disposed parallel to a director plane and is selected from the group consisting essentially of steel, titanium, nickel and alloys thereof, said high modulus reinforcing material is selected from the group consisting essentially of boron, silicon carbide, titanium boride, aluminium diboride and magnesium diboride, said high modulus reinforcing material being in the form of flakes or bands and disposed parallel to the director plane.
 2. The composite material as defined in claim 1, wherein the matrix is of a material which provides good cohesion between the resistant material and the high modulus material.
 3. The composite material as defined in claim 1, wherein the resistant material is titanium, the reinforcing high modulus material is silicon carbide flakes, said composite material is prepared so that a physicochemical interaction develops between the titanium and the silicon carbide.
 4. The composite material as defined in claim 1, wherein the resistant material is titanium, the reinforcing material is a band comprising a silicon carbide surface and a core selected from the group consisting essentially of molybdenum and titanium, said composite material is prepared so that a physicochemical interaction develops between the titanium of the resistant material and the silicon carbide. 